The present invention relates to granulation of compost materials and more particularly, the present invention relates to a method of producing high quality granulated compost and multiple component compost granules for fertilizer applications.
The granulation art is a mature art and recently significant advances have been made by Derdall et al., U.S. Pat. No. 5,460,765, issued Oct. 24, 1995 and subsequently by Phinney in U.S. Pat. No. 6,013,209, issued Jan. 11, 2000.
With reference to Derdall et al., this disclosure provided teachings which advanced this art by demonstrating that an ultra fine powder (xe2x88x92200 mesh) does not cause nucleation of the powder, but rather results in adhesion of the material to large round pellets. This process is not unlike the proverbial growth of a snowball. The technique invented by Derdall et al. clearly provides excellent process control needed to effectively maximize the contact of fine particles with binder. As a result, binder additions of 5% and less are routinely used where the previous art required approximately double this amount. As is evident, if the amount of binder can be reduced, the amount of feedstock in the particle can be increased, which, in turn, provides an improved pellet or granule.
The Derdall et al. process established that a large significant crystal or seed is critical to perform the granule formulation in one step. Although this is a significant advance in the art, it does not contemplate granulation of materials directly on the pan. If a mixture of material which contains the feedstock to be granulated and moisture is provided in a pre-moistened mixture, there is effectively no seed or nucleating agent present. This material is then used directly on the pan containing the powdered feedstock to facilitate growth of a granule.
Derdall et al. advanced the granulation art significantly by demonstrating that powdered material could be granulated, provided a seed material was used as an initiator to grow the particle. Prior to the efforts by Applicant, Derdall et al. effectively taught the state-of-the-art and is an extremely useful process when seed material can be used to form a granule. Such granules have obvious cores in the center of the granule.
In the art, it has been generally recognized that any particle greater than +150 mesh and xe2x88x92100 mesh causes over-nucleation on the pan which inevitably leads to the particles sticking together in agglomerated groups. This led to the conclusion that in order to make a strong enough pellet a binder must be present in an amount generally between 4% to 10% in order to effect proper adhesion of the materials into a consolidated particle.
The Derdall et al. reference clearly teaches that there are stability problems with the process if one uses a seed which exceeds certain size parameters. In summary, Derdall et al. was the first to provide a process for granulating powdered material.
Turning to the Phinney disclosure, an advance over what was initially demonstrated in Derdall et al., was provided. In the Phinney patent, it was found that if one were to use a nucleating agent, which is effectively a powder in the size range of xe2x88x9235 mesh to 150 mesh, a seed could be grown and composed of the same material of the final product in a size distribution of approximately xe2x88x928 mesh to +4 mesh. The distinction between Derdall et al. and the Phinney patent resides in the fact that Phinney recognized that a seed was not initially required to effect granulation; the seed could be formulated by using an initial nucleating material in a powder form to first formulate a seed which could be later grown in further granulation operations. This resulted in significant advantages in terms of the final product quality. One of the chief advantages is directed to particle strength and uniform material accretion about the seed. In view of the fact that the nucleating material used was effectively infinitesimally small, the Phinney granules effectively had no core relative to the particles produced by the Derdall et al. method. In this manner, the particles produced according to the Phinney methodology provide particles having a uniformed and uninterrupted cross-section. Accordingly, a higher feedstock content could be included in each granule or pellet.
The Phinney and Derdall et al. references have provided significant instruction in the granulation art with respect to materials having fairly high bulk density. In the case of these references, sulfur has been illustrated as an example that could be granulated. Sulfur has a fairly high bulk density, approximately of the order of between 30 and 35 pounds per cubic foot (lbft-3). This bulk density presents a particle size of between about 180 mesh and 300 mesh. At this bulk density, there is sufficient mass to permit the granulation of the product. It has been found that this is not the case with all materials and problems can arise when the bulk density drops from the value indicated for sulfur to, for example, compost. The granulation of compost material presents unusual complications. Compost material, when pulverized, is extremely lightweight, hydrophobic and the individual particles repel one another by electrostatic interaction. The bulk density of compost is approximately between 20 lbft-3 to about 25 lbft-3, which corresponds to a particle size of generally between about 240 mesh to about 400 mesh. This powder level, taken together with the properties of compost, the techniques established in the prior art and particularly, the Derdall et al. and Phinney references, require modification under certain circumstances to effect granulation of this valuable agronomic compound.
The proposition of granulating compost has been proposed in the prior art as has the concept of coating or otherwise encapsulating seeds for the protection of the seed until such time that it is desired for this to germinate.
Typical of the prior art in this area includes the process set forth in U.S. Pat. No. 3,905,796, issued September 1975, to Ghelfi. The disclosure teaches a process for dehydrating manure based fertilizers where a homogenous and durable pulp is granulated and dried.
U.S. Pat. No. 4,082,532, issued to Imhof, Apr. 4, 1978, discloses a process for manufacturing extruded cattle manure pellets where the cattle manure is mixed into a pulp and contains a moisture content between 50 to 55% by weight. The material is extruded to form strands which are subsequently further broken down into smaller forms. In this reference and the above-mentioned reference, there is no discussion as to the use of further agricultural additives to the compost and very few details concerning the granulation. It has been discovered in the instant application that once the compost material has been dried and pulverized, it is difficult to wet this material in the absence of a surfactant. The references discussed thus far do not touch on this issue whatsoever and only provide generic teachings with respect to the granulation.
Davis, in U.S. Pat. No. 5,043,007, provides a process for the production of fertilizer or the fertilizer is binder free fertilizer. The disclosure provides for a seed material and a primary and secondary nutrient sources which are put into a blender under heat until the slurry is formed. The slurry is transferred to a dryer and the product dried under vacuum and thereafter cooled to produce a granular or semi-granular fertilizer with a core of a seed material and a coating of a secondary nutrient crystallized thereabout.
In U.S. Pat. No. 5,725,630, issued to Roberts et al., Mar. 10, 1998, a fertilizer plant is set forth as well as a dry granular fertilizer. The granular fertilizer contains a C1-C6 alkanoic acid or salt of this-compound added on to a dry carrier form of granular fertilizer. This is a simple coating process and does not provide a granule having ancillary or auxiliary fertilizer compounds granulated uniformly therein.
Turning to additional prior art in the fertilizer/seed encapsulation field, U.S. Pat. No. 4,779,376, issued to Redenbaugh, Oct. 25, 1998, discloses an encapsulation method for a botanical seed where the seed is encapsulated in a water saturated hydrogel capsule.
Johnson et al., in U.S. Pat. No. 3,648,409, issued Mar. 14, 1972, discloses a herbicide resistant carrier process for manufacturing the product. There is disclosed a method and a herbicide resistant wafer encases a seed and a mixture of water soluble nutrient binder vermiculite and activated charcoal, which is subsequently compressed into a desired shape, in this case, a wafer.
Other references generally related to seed coating or encapsulation include U.S. Pat. Nos. 4,759,151, 5,849,320, 3,950,891, 3,905,152, 5,435,821 and 3,651,772.
The prior art when taken singly or in combination does not provide specific teaching for the granulation of compost powder material which may include auxiliary fertilizers, time release materials, or other suitable additives well known in the granulation art. Further, the fact that there is no teaching with respect to the granulation of the compost, it is also submitted that the art reviewed fails to provide a granulated product having a seed encapsulated therein while still maintaining desirable properties such as roundness, particle break strength, rate of salvation, etc. It would be desirable to have a method as well as a product directed to enhancing the fertilization of soils where the fertilizer consists of compost material in a powdered form at the xe2x88x92150 mesh level or less which may be co-granulated with additional fertilizer materials such as some of the known fertilizers discussed hereinafter without the problem of the hydrophobicity of the compost powder. The present invention satisfies these needs as well as others.
One object of the present invention is to provide an improved method for granulating compost powder in the absence of a nucleating material, seeding material, or other initiator. A further object of one embodiment of the present invention is to provide a method of encapsulating, by granulation, agricultural seeds for the purpose of encapsulating the seed.
One object of the present invention is to provide a method of granulating compost material, comprising the steps of:
providing a source of dried pulverized compost material in a size distribution of 90% of less than xe2x88x92150 mesh;
forming a moist mixture of dried pulverized compost and binder containing moisture, the mixture containing up to 11% by weight moisture in the mixture;
mixing the mixture sufficiently to invert the hydrophobicity of the pulverized compost material, where the pulverized compost material absorbs the moisture from the binder and forms a flowable compound;
granulating the mixture into granules on the pan by contact of the mixture with additional binder material and a surfactant; and
forming compost granules in a size distribution of 3 mesh to 12 mesh.
Advantageously, the compost is sterilized when heated and pulverized and, therefore, odor and pathogens are not a concern. This also allows the compost from any source to be used including animal, plant or combinations of these.
In view of the hydrophobicity of the powder compost, it has been found that by providing a free moisture content of up to 11% by weight on the pan that the process will be viable and produce granules. In this manner, it is an essential feature of the present case to include a surfactant to reduce the surface tension of the compost dust and thus allow granulation to occur directly on the pan in the absence of any nucleating material or other particle growth initiators. Suitable surfactants will be appreciated by those skilled in the art. This process embodiment is effective for granulating compost in a wide percentage by weight basis.
The art has established the use of a nucleating agent for granulating feedstock material under xe2x80x9cdryxe2x80x9d conditions. This was established in the Phinney U.S. patent discussed supra. Reference to this type of condition was also made in the Derdall et al. patent. In further advances made by Phinney, and particularly those set forth in PCT Publication, PCT/CA 99/00300, (International Publication No. WO 99/54029 published on Oct. 28, 1999), it was established that pan granulation could be effected by simply providing a wet mixture (a mixture containing moisture, feedstock and surfactant) and contacting this wet mixture with feedstock within the pan. This resulted in the formation of granules directly on the pan in the absence of a nucleating agent or seed. In this manner, the granulation could be effected by eliminating the step of formulating a seed.
As briefly discussed hereinabove, compost presents new complications for the process designer in view of the properties of the compost. The bulk density has been mentioned above as well as the other properties which complicate granulation procedure. In view of the properties, direct pan granulation such as that established in the PCT publication is not convenient. Considering the other existing dry methodology, particularly pre-formulation of a seed by a nucleation unit operation, this also is unsatisfactory in view of the properties of the compost. The material is not conducive to the preparation of a nucleating material in view of the size distribution of such agents. This is partly due to the fact that pulverized compost presents the hydrophobicity problem as well as the electrostatic interaction complication. Simply by these properties, a material that is inherently self-repulsive and hydrophobic, cannot effectively be granulated into a pellet as a nucleating material and most certainly not as a seed with the ultimate goal of generating a granule acceptable in the marketplace.
In the instant case, the full recognition of the compost properties together with extensive engineering experience have been combined to overcome the inherent complications with compost granulation. It is well accepted that the Derdall et al. method as well as the Phinney method have resulted in significant advances in the art. Despite this, neither method is particularly well suited to the granulation of compost, since these references were primarily concerned with the granulation of higher bulk density materials having further properties different from compost.
In the case where it would be desirable to form a granule of a larger size for a particular use, a multiple phase granulation process may be followed. Larger granules are applicable in the golf course fertilizer industry. It is desirable to have larger granules for time release purposes. As it has been established in the art by Derdall et al. and Phinney, the material being granulated on the pan will equilibrate at a certain size distribution, depending on pan rotation velocity, pan tilt and pan pitch among a host of other factors. As such, there is a need, under certain circumstances, to employ a second pan for further material accretion.
Accordingly, in accordance with a further object of one embodiment, there is provided a method of granulating compost material, comprising the steps of:
providing a source of dried pulverized compost material in a size distribution of 90% of less than xe2x88x92150 mesh;
forming a moist mixture of dried pulverized compost and binder containing moisture, the mixture containing up to 10% by weight moisture;
mixing the mixture sufficiently to invert the hydrophobicity of the pulverized compost material, where the pulverized compost material absorbs the moisture from the binder and forms a flowable compound;
granulating in a first stage the mixture into granules on the pan by contact of the mixture with additional binder material and a surfactant, the granules being in a size distribution of between 3 mesh and 12 mesh and including at least a fraction of particles in a size distribution of between 8 mesh and 12 mesh;
granulating the fraction of particles 8 mesh and 12 mesh in a second stage by contact with the mixture and additional binder; and
forming compost granules in a size distribution of between xe2x88x923 mesh and +8 mesh.
In some situations, it is desirable to have a fairly sizeable granule beyond that which is set forth in the above-captioned object. From a procedural point of view, the xe2x88x923 mesh to +8 mesh granules may be further grown to a size distribution of xc2xdxe2x80x3 or greater. This can be accomplished by making use of a drum granulator. Similar unit operations such as binder addition, surfactants, blending with the binder, would be observed in the drum to achieve xc2xdxe2x80x3 granule growth.
As it will be immediately appreciated to those skilled in the art, it does not matter the specific order of binder surfactant being added to the granulating pan, the point here is that the material on the pan must have an adequate supply of surfactant to effect granulation together with binder to adhere the compost mixture. In this manner, the binder surfactant may be mixed and added to create up to 11% by weight moisture content or these may be added simultaneously separately. Variations, again, will be appreciated by those skilled in the art.
As a further application, the technology set forth herein fits well with the encapsulation of agricultural seed material and accordingly, a further object of the present invention according to a further embodiment is to provide a method of encapsulating an agronomic seed with compost material into a granulated pellet, comprising the steps of:
providing a source of dried and pulverized compost material, pulverized to dust in a size distribution of 90% of less than xe2x88x92150 mesh;
providing a source of agronomic seeds;
forming a moist mixture of dry pulverized compost and binder containing moisture, the mixture containing up to 11% by weight moisture;
mixing the mixture sufficiently to invert the hydrophobicity of the pulverized compost material, where the pulverized compost material absorbs the moisture from the binder and forms a flowable compound;
providing a granulation pan;
contacting the pan with the agronomic seeds;
contacting the pan with the mixture; and
granulating the mixture about the seeds on the pan by contact of the mixture with the seeds; and
forming pellets of encapsulated agronomic seeds with compost.
Any seed material could be encapsulated. Examples of suitable seeds which would particularly benefit from encapsulation are the light seeds that typically are air dropped including canola seeds, canary, rape seeds, inter alia. This is problematic since the seeds, being fairly light are often blown off course relative to their intended location and this adds significant costs to the farmer. Further, in many countries xe2x80x9cbroadcastingxe2x80x9d of seeds is now becoming an unpopular procedure for planting crops. By encapsulating such seeds, mass is added, the seed is protected and there is inherent spacing afforded by the granulation material between seeds when planted. One of the particularly attractive features of seed encapsulation is that the compost material effectively acts as a fertilizer for the seed and thus provides a seed with its own fertilizer. Further, by the provision of adding further suitable fertilizer materials discussed herein, a most desirable product results.
Fertilizer salts cannot be placed too close to the seed. The osmotic pressure of these salts is too high and the seeds will not germinate. The 1-1-1-1 in compost is in humates which the plant readily receives without changing the osmotic pressure.
Advantageously, the methodology has resulted in greater than 30% of the granules containing a single seed. Further, encapsulation automatically provides the seed with nutrients and humates and considering the size of the particle (6 to 8 mesh) small seeds are not wasted during planting. The coating also ensures flowability of seeds that would otherwise not flow to permit greater ease in handling and transportation.
Typical over seeding costs for Canada could be as high as 50%. With seed costs of $500 per ton, a 50% saving is substantial. It is well known in farming that the seeds should have uniform spacing in order to maximize yields. Too many plants too close together reduces yields significantly. The present invention eliminates this wastage to provide a cost effective method of seeding.
In another application, the agronomic seed may be replaced by a suitable fertilizer material. Accordingly, a further object of another embodiment is to provide a method of granulating compost material, comprising the steps of:
providing a source of dried and pulverized compost material, pulverized to dust in a size distribution of 90% of less than xe2x88x92150 mesh;
providing a source of a fertilizer material as a seeding agent;
forming a moist mixture of dry pulverized compost and binder containing moisture, the mixture containing up to 11% by weight moisture;
mixing the mixture sufficiently to invert the hydrophobicity of the pulverized compost material, where the pulverized compost material absorbs the moisture from the binder and forms a flowable compound;
providing a granulation pan;
contacting the pan with the fertilizer material;
contacting the pan with the mixture; and
granulating the mixture about the fertilizer material on the pan by contact of the mixture with the seeding agent; and
forming pellets of encapsulated fertilizer material with compost.
A further object of one embodiment of the present invention is to provide a granulated compost granule, comprising:
an agronomic seed; and
compost material granulated therearound.
An even further object of one embodiment of the present invention is to provide a composite granule, comprising:
a homogenous blend of compost and fertilizer.
A still further object of one embodiment of the present invention is to provide a composite compost granule, comprising:
a central fertilizer core; and
compost material granulated therearound.
The advantages ascribable to the products formed in accordance with the methods are numerous and include the following:
a. the product is granulized dry;
b. particle size can be customized for specific uses;
c. transportation is greatly simplified relative to conventional compost;
d. the granules assist in soil moisture retention by building up humic content thus improving tolerance against drought while providing benefit to crop growth;
e. run-off is prevented together with concomitant nutrient loss;
f. soil exchange and buffering capacity are improved;
g. product is non-toxic and non-burning;
h. provides sustained long-term benefit to the soil as opposed to relatively short term benefit of chemical fertilizers;
i. provides a source of water insoluble nitrogen that is released over a long period of time;
j. provides the opportunity to combine both positive aspects of organic and inorganic fertilizer synergistic benefit in view of the co-granulation; and
k. simplified application which is more precise and less wasteful relative to broadcasting.
A still further object of one embodiment of the present invention is to provide a composite granule, comprising:
an agronomic seed in a size distribution of between +35 mesh and xe2x88x928 mesh;
composite material layered thereon forming a granule having a seed encapsulated therein in a size distribution of between 6 mesh and 8 mesh.